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Monday, May 23, 2011

The evolution of complexity without natural selection

There is a very interesting report in Nature this week (see the BBC story, if you can't access Nature) about the evolution of complex life and the role of natural selection in that. The BBC writes

A comparison of proteins across 36 modern species suggests that protein flaws called "dehydrons" may have made proteins less stable in water.

This would have made them more adhesive and more likely to end up working together, building up complex function.

The Nature study adds weight to the idea that natural selection is not the only means by which complexity rises.

These flaws are a particular aspect of proteins that make them less likely to do their assumed original or 'proper' job as well as the normal form of the protein would. This molecular deficit makes proteins stickier and more likely to adhere to each other. The authors suggest that this can enable more complex molecular interactions, and hence more complex living forms.

The analysis showed that organisms with smaller populations - such as humans - had accumulated more of these defects than simpler organisms with vastly higher population numbers.

One of the authors, Michael Lynch, has been trying to persuade biologists that classical Darwinian natural selection is not the only way that complex traits can be enabled. The other author, Ariel Fernandez, is an expert on the particular biochemical aspects of these modified proteins. If a population is small enough, traits that are not quite as 'good' (in terms of their darwinian fitness) as some other version of the trait in the population can nonetheless proliferate and even displace the 'better' one. This works when the supposed deficit is small relative to the best-available, and the population is small. The consequent advance in frequency of the less robust forms can lead to new traits--such as the aggregation of similarly deficient proteins to lead to more complex structures and hence new or more complex traits.

This is not an argument that classical kinds of natural selection don't or can't occur, but it is an argument that nature is not always relentlessly perfecting and purifying what exists. So it is a challenge to the kind of universal selectionism that we often see and hear stated as 'the' theory of evolution. Of course, if something advances, an ardent Darwinian can say that, however indirectly, this variant was in a sense the best after all, or that the new complex trait would not evolve without being favored by selection. So a Darwinist would argue that it is wrong to refer to these as 'flaws' in molecules, just as, from an evolutionary point of view, humans' poor night vision, worse than that of, say, owls, is not a 'flaw': in our evolutionary history, it was the best available.

We won't delve into that argument, which involves definitions of terms, ideas very hard to test scientifically, short-term ideas assumed to apply steadily in the long term, as well as stubbornly held ideological views about evolution.

But we will point out that the idea of Lynch and Fernandez relates to a major interest of ours, here on MT here and in the book after which we named this blog: it relates to what we have called cooperation in the nature and evolution of life. Evolutionary success has involved at least as much successful interaction among cooperating units--in this case 'defective' proteins--as it has involved relentless all-seeing selective competition. Selection and cooperation exist, perhaps at all levels of life. The major question for biologists who want to understand life rather than just assert an ideology about it, is to understand how these two factors, along with many aspects of chance, explain how life works and how it got that way.

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